Conventionally, the key elements of the scan system are a photosensor, an illumination lamp such as a fluorescent lamp or an array of light emitting diodes, a set of lenses, a motor, and a power supply. The scanning operation of the prior art scan system is described as follows: The illumination lamp illuminates a flat document, or a bound document, such as a book. The image is reflected along an optical axis, projected through lens and reflected through mirror onto the surface of a photoreceptor drum or a charge-coupled device, CCD. The scanning operation is satisfactory for most applications, but is less than satisfactory for those systems which afford a book copying capability. Because of a binding edge of a book, the sensed light intensity of the binding edge is different.
Furthermore, the copying of non-planar originals, such as bound books, presents a problem because it is difficult to copy the information adjacent the binding of the book. The difficulties of reproduction in the binding area results from the portion of the book adjacent the binding being lifted away from the original image plane, which is usually defined by a planar transparent plate. The quality of the reproduction decreases in relation to increasing distance of the original image from the image plane. The lack of clarity and/or distortion in the copy results from several factors including 1) the projected image becomes increasingly out of focus as the original is scanned in the central binding area; 2) the illumination becomes less than optimal in the spine area; 3) there is compression of the image data along the scan length; and 4) there is degradation of the definition of the image data resulting from the original image being disposed at an angle to the image plane.
Nowadays, there are some inventions utilizing automatic electronic image correction technique to correct the book curve caused by the binding edge of a book. Although the book scanner system such as OMNISCAN 5000TT/5100TT is convenient and easy to digitize and/or copy books and bound documents and guarantees that the book bindings are not damaged, however, it is too expensive to use the instrument for the general public.
Another approach is to modify the platen to have a sloping edge portion so that the bound part of the book is placed in a corner position so that the entire surface of the page being copied is in intimate contact with the platen surface. An example of such a system is disclosed in U.S. Pat. No. 3,775,008. These systems have a disadvantage. The magnification range is limited because of restriction on scanner movement in the sloping corner edge.
In addition, the illumination lamp generally is a fluorescent lamp; however, the light intensity of the two ends of the fluorescent lamp is smaller than the central part thereof. The prior art method and apparatus is to increase the length of the fluorescent lamp to increase the usable scan zone. Thus, the volume of the scan system must be increased.
It is therefore attempted by the applicant to deal with the above situation encountered with the prior art.